Hi epaulino4! Didn't I see your question asked on The Lonely Planet Thorn Tree message board? That person wanted to get to Barajas by 5:30am on a Saturday. Anyway, here was my answer there:
rosflute, are you checking out of a hotel on Saturday morning or staying with a friend? I ask because, as klaush says, you can get the hotel desk to arrange to have a taxi for you at whatever time you want to leave (no later than, I'd say, 4am) but just so you know the taxis charge more to have a car called. The meter starts when they receive the call and not when they arrive to pick you up (that's my understanding, anyway). While it's ALWAYS possible, you shouldn't have any traffic problems at that time of night/morning.
Not sure what shuttle to which you were referring above - maybe the AeroCity shuttle or maybe a hotel shuttle. If a hotel shuttle, I doubt they run that early. Same goes, probably, for AeroCity.
And you ask above:
Is a taxi the only option? what other modes of transportation besides taxi will be available?
I'd say yes, your taxi is your only viable option. The metro does't start until 6am and the busier bus lines also don't start until 6am. I don't know about the AeroCity shuttle either but I seriously dout they start as early as you'll want to leave for the airport (between 4 and 4:30am).
Saludos, MadridMan
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